The use of certain dialkyldialkoxysilanes as stereomodifiers in Ziegler-Natta type catalysts is known in the polymerization of various olefinic monomers. The preparation of specific silane compounds of this type is disclosed by U.S. Pat. No. 4,958,041 to Graefe et al., wherein said silanes are represented by the general formula ##STR1## in which R.sup.1 and R.sup.2 each represent an alkyl or cycloalkyl group having 3 to 10 carbon atoms and R.sup.3 is independently selected from alkyl radicals having 1 to 5 carbon atoms. Graefe et al. teach that these materials are selectively produced by reacting a tetralkoxysilane or a monoorganotrialkoxysilane with a Grignard reagent having the structure. e.g., R.sup.1 MgCl. This prior art citation specifically teaches away from the use of the typical solvents employed in Grignard reaction, such as tetrahydrofuran, in favor of dialkyl ethers, such as methyl-tert-butylether, in order to attain essentially quantitative yields of the products. The patent to Graefe et al. does not teach or suggest the formation of the cycloalkoxysilanes of the present invention and applicants have not been able to find reference to the particular compounds, described infra, in the open literature.